Now that most users download PRISM data in BIL format, we will stop producing data in ASCII GRID format as of January 1, 2022. The 1991-2020 30-year normals will remain available in both formats, but the time series grids will be available in BIL format only. Note that if you have a particular need for it, the BIL grids can be converted to ASCII GRID format using the open source GDAL raster processing software, among other tools.